Storage area networks (SANs) enable initiators or host computers to login to storage devices and perform a sequence of commands, such as inquiries, report logical unit numbers (LUNs), read, write, etc. Some hosts logout when the command sequence has completed. Other hosts, however, do not logout even when the command sequences are finished. Storage devices have limited resources for processing host logins and thus limit how many active hosts are logged in at any one time.
Some storage devices have methods of managing the number of host logins. A least recently used (LRU) algorithm is one method for managing host logins. In this method, hosts are managed according to “first in first out” (FIFO) rules. When the login capacity is full and a new host is attempting to login, the oldest host is removed.
Historically, the LRU algorithm has been sufficient for some SANs. However, as fibre channel (FC) SANs have grown in maturity and the number of hosts and storage devices connected to the SAN has increased, the LRU algorithm is not effective for managing host logins. Specifically, such LRU algorithms provide equal treatment and access to hosts authorized to perform read/write operations and hosts authorized to access the storage device but not perform such read/write operations. Some host do not have read/write access to the storage device, but still need to login into the storage device and perform a limited subset of commands, such as inquiry, report LUNs, mode/log sense, etc. These hosts are referred to as non-authorized.
One problem occurs when a large number of non-authorized hosts login and cause authorized hosts to be prematurely retired from the storage device. In some instances, FC SANs experience large numbers of simultaneous login attempts or login storms. During these login storms, numerous hosts simultaneously attempt to login in as the result of a scheduled process running at some frequency or as a result of an event or perturbation in the SAN (example, a change notification from the fabric due to a node either connecting or disconnecting from the fabric/switch). During these login storms, authorized hosts are retired from the storage device or restricted from timely accessing the storage device.